The active cathode materials used in rechargeable lithium cells include materials based on lithium manganese dioxide, on which many experiments have been conducted. Some have been found to be unrechargeable or rechargeable to only a small degree, such as Li.sub.2 MnO.sub.3 and derivatives of .beta.-MnO.sub.2 and .gamma.-MnO.sub.2. The specific cell capacity decreases rapidly after a few cycles in the case of materials with a spinel structure such as LiMn.sub.2 O.sub.4, Li.sub.1-x MnO.sub.4, Li.sub.1s+x Mn.sub.2 O.sub.4 (described in U.S. Pat. No. 5,196,279) and .lambda.-MnO.sub.2. Nevertheless there are substances with a stable capacity on cycling but having a discharge voltage below 3 volts, such as the substance derived from .alpha.-MnO.sub.2 described in French patent 2 644 295 or that derived from Li.sub.2 MnO.sub.3 described in French patent 6 656 957. The energy per unit volume of cells using these substances is low.
Materials which can be cycled electrochemically having mean discharge voltages above 3.5 volts are known, such as the lithium metal oxides LiCoO.sub.2, LiNiO.sub.2 and LiNi.sub.1-x Co.sub.x O.sub.2. The oxides of nickel and cobalt have the disadvantage of being much more costly than manganese dioxide and they are extracted only in hazardous geographical regions.